This invention relates to a heat-sensitive stencil, to a process of preparing a stencil printing master and to a stencil printer using the heat-sensitive stencil.
One known heat-sensitive stencil is composed of an ink-permeable thin paper serving as an ink port and a thermoplastic resin film bonded with an adhesive to the port. The stencil is heated imagewise by, for example, a thermal head to perforate the heated portions of the thermoplastic resin film, thereby obtaining a printing master for reproducing images by mimeographic printing. The conventional stencil, however, poses problems because (1) the adhesive tends to be accumulated in interstices between fibers to form xe2x80x9cfinsxe2x80x9d which prevent the thermal perforation during the master forming step and the passage of an ink during the printing step, (2) the fibers per se prevent smooth passage of an ink and (3) the paper port is relatively expensive.
To cope with the above problems, JP-A-54-33117 proposes a stencil-having no paper port and composed stantially only of a thermoplastic resin film. While this stencil can completely solve the above-mentioned problems, a new serious problem arises; i.e. it is necessary to significantly increase the thickness of the stencil in order to obtain satisfactory stiffness required for transferring the stencil master during printing stage. An increase of the thickness results in the lowering of the thermal sensitivity.
U.S. Pat. No. 5,843,560 discloses a heat-sensitive stencil having a porous resin layer formed on a thermoplastic resin film. This stencil has been found to be able to solve the above-described problems but to cause a problem because of insufficient tensile strength.
JP-A-H10-147075 discloses a heat-sensitive stencil having a porous fibrous layer over a surface of a porous resin layer. The fibrous layer has been found to improve the tensile strength of the stencil but to adversely affect the print image quality.
It is an object of the present invention to provide a heat-sensitive stencil which has a high stiffness, a high tensile strength and gives a high quality print.
Another object of the present invention is to provide a heat-sensitive stencil of the above-mentioned type which can exhibit a high resistance to inter-layer delamination.
In accomplishing the foregoing objects, there is provided in accordance with one aspect of the present invention a heat-sensitive stencil which comprises a thermoplastic resin film, a porous resin layer provided on said thermoplastic resin film, an ink permeable, water soluble resin layer provided on said porous resin layer, and a fibrous porous layer provided on said water soluble resin layer.
In another aspect, the present invention provides a heat-sensitive stencil which comprises a thermoplastic resin film, a porous resin layer provided on said thermoplastic resin film, a fibrous porous layer provided on said water soluble resin layer, a thin resin layer provided between said thermoplastic resin film and said porous resin layer, and imagewise perforations provided in said stencil and each having an area of at least D xcexcm, wherein said porous resin layer has pores exposed to a surface thereof to form a multiplicity of openings, wherein the total area of said openings is Y% of the area of said surface, and wherein D and Y have the following relationship:
D=(61xe2x88x92Y)/0.0063.